Glossary of Spring Terminology
Active coils (n): Those coils which are free to deflect under load.
Closed ends: Ends of compression springs where pitch of the end coils is reduced so that the end coils touch.
Closed and ground ends: The closed ends of a spring, ground to provide a flat plane.
Close-wound: Coiled with adjacent coils touching.
Coils per inch: See Pitch.
Deflection: Motion of spring ends under the application or removal of an external load (P).
Elastic limit: Maximum stress to which a material may be subjected without permanent set.
Free angle: Angle between the arms of a torsion spring when the spring is not loaded.
Free length (L): The overall length of a spring in the unloaded position.
Heat setting: Fixturing a spring at elevated temperature to minimize loss of load at operating temperature.
Helix: The spiral form of compression, extension, and torsion springs.
Hooks: Open loops or ends of extension springs.
Hydrogen embrittlement: Hydrogen absorbed in electroplating or pickling of carbon steels, tending to make the spring material brittle and susceptible to cracking and failure; particularly under sustained loads.
Initial tension: The force that tends to keep the coils of an extension spring closed and which must be overcome before the coils start to open.
Load (P): The force applied to a spring, usually in pounds or Newtons.
Loops: Coil-like wire shapes at the ends of extension springs that provide for attachment and force application.
Mean coil diameter (D): Outside spring diameter (O.D.) minus one wire diameter (d).
Modulus in shear or torsion (G): Coefficient of elasticity used for extension and compression springs.
Modulus in bending (E): Coefficient of elasticity used for torsion springs.
Moment (M): See Torque.
Open ends, not ground: End of a compression spring with a constant pitch for each coil.
Open ends, ground: “Open ends, not ground” followed by an end-grinding operation.
Passivating: Acid treatment of stainless steel to remove contaminants and improve corrosion resistance.
Permanent set: A material that is deflected so far that its elastic properties have been exceeded and it does not return to its original condition upon release of load is said to have taken a “permanent set”.
Pitch (p): The distance from center to center of the wire in adjacent active coils. Recommended practice is to specify number of active coils rather than pitch.
Rate (R): Change in load-per-unit deflection, generally given in pounds per inch.
Remove set: The process of closing to solid height a compression spring which has been coiled longer than the desired finished length, so as to increase the apparent elastic limit.
Residual stress: Stresses induced by set removal, shot peening, cold working, forming or other means. These stresses may or may not be beneficial, depending on the application.
Set: Permanent distortion which occurs when a spring is stressed beyond the elastic limit of the material.
Solid length: Length of a compression spring when under sufficient load to bring all coils into contact with adjacent coils.
Spring index: Ratio of mean coil diameter (D) to wire diameter (d).
Squared and ground ends: See Closed and ground ends.
Squared ends: See Closed ends.
Stress range: The difference in operating stresses at minimum and maximum loads.
Stress relieve: To subject springs to low-temperature heat treatment so as to relieve residual stresses.
Shot peening: A cold-working process in which the material surface is peened to induce compressive stresses and thereby improve fatigue life.
Torque (M): A twisting motion applied to torsion springs which tends to produce rotation. Equal to the load multiplied by the distance (or moment arm) from the load to the axis of the spring body. Usually expressed in inch-pounds.
Total number of coils (N): Number of active coils (n) plus
Reference Standards
The various reference standards defined by the Bureau of Indian Standards applicable for the manufacturing of Springs. Wireforms and Sheet Metal Components and the use of various materials like – Steel, Copper, etc. are mentioned below with the copy of the guidelines and amendments made in the same till date for reference purpose. Wirecom India follows these guidelines while manufacturing its quality springs.
